The calculation of the amplitudes for the subprocess \(\gamma ^* q_a\rightarrow P q_b\)  to twist-3 accuracy
is a straightforward generalization of our calculation of the process \(\gamma q_a\rightarrow \pi ^0 q_a\)  [1]}.
In the definitions of the soft pion and nucleon matrix elements we are using light-cone gauge: the
plus component of the gluon field is zero. All possible Wilson lines become unity in that gauge.
It is to be stressed that our method for calculating the subprocess amplitudes is similar to the light-cone
collinear factorization approach advocated for in [2]}, [3]} for the case of electroproduction
of transversely polarized vector mesons.
